Areas of Expertise:

Education:

Ph. D., University of California, Santa BarbaraM. S., University of Massachusetts, AmherstB. S., Rutgers University

Background:

I am a limnologist and ecologist with relatively broad interests. A major theme in my research has been to understand the roles that interactions among aquatic populations (primarily phytoplankton and zooplankton) play in population and community dynamics within lakes. I am also interested in how these interactions impact the overall functioning of aquatic ecosystems. The approach that I take to questions relies very heavily on field experimentation, and I am very interested in assessing how well such experiments inform us about processes in nature.

Lately, we have been focusing most of our research attention on the ecology of cyanobacteria, the most important group of freshwater phytoplankton with respect to degradation of water quality in lakes and reservoirs. Harmful blooms of freshwater phytoplankton (so-called HABs) nearly always involve cyanobacteria, which produce a variety of compounds with acute and chronic toxicity to humans and other terrestrial animals.

Research Interests:

Interactions between Daphnia and cyanobacteria in eutrophic lakes - We continue to extend previous counter-intuitive results regarding the impact of Daphnia grazing on supposedly-inedible cyanobacteria (blue-green algae). This research has implications for the control of nuisance cyanobacteria in productive lakes. We have demonstrated that Daphnia pulicaria collected from lakes with high concentrations of cyanobacteria are better able to grow on a diet of 100% toxic cyanobacteria than individuals of the same species collected from lakes with little or no cyanobacteria. More recently, we demonstrated in field experiments that the ability of a Daphnia population to supress toxic blooms of phytoplankton is largely driven by the presence of Daphnia genotypes that are tolerant of cyanobacterial toxins. Our recent work is a collaborative effort with scientists at Auburn University.

Zebra mussels and toxic algal blooms in lakes - We are investigating the link between zebra mussel invasion and the incidence and severity of cyanobacterial blooms in lakes. We have conducted a series of large-scale field experiments to determine the functional relationship between zebra mussel abundance and phytoplankton biomass and species composition. We have demonstrated that zebra mussels increase the abundance of Microcystis aeruginosa, a toxic phytoplankton species, and the concentration of microcystin toxin, in lakes with low to moderate nutrient levels. In direct contrast, zebra mussels suppress this same species when nutrient levels are increased. These findings have potentially radical implications for both the field of limnology and for the management of water quality, although the precise mechanisms driving the effect reversal remain to be uncovered. We have collaborated with scientists at the Great Lakes Environmental Research Laboratory (NOAA) on zebra mussel-Microcystis interactions.

High Sierra Experimental Lakes - We are examining how the removal of an exotic predator influences population, community and ecosystem dynamics at the whole-lake scale. High-elevation lakes in the Sierra were once fishless, with a unique set of planktonic and benthic species that are driven locally extinct by the stocking of exotic trout. From a set of whole-lake manipulations, we have demonstrated that the probability of recovery from local extinction is much lower for sexually-reproducing copepods than for asexually-reproducing Daphnia. We have also demonstrated that mate limitation (an Allee effect) reduces the re-establishment probability of sexually-reproducing copepods, despite the presence of viable resting eggs in the sediment. This work represents a collaboration between MSU and the Sierra Nevada Aquatic Research Laboratory (UCSB).

Meta-analysis - I was part of a working group sponsored by the National Center for Ecological Analysis and Synthesis examining issues regarding the application of meta-analysis to ecological questions. Meta-analysis, the quantitative synthesis of published experimental results, holds great promise for prediction and generality, but the techniques used in classical meta-analysis require conceptual modification before being applied in ecology. A recent meta-analysis we conducted uncovered consistent evidence of a Type 3 functional response in Daphnia, which we suspect may extend to other filter feeders.